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Pivot-shift test
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The pivot-shift test[1] is one of the three major tests for assessing anterior cruciate injury or laxity, the other two being the anterior drawer and Lachman test. However, unlike the other two, it tests for instability, an important determinant as to how the knee will function.[1] In fact, it is instability, not simply the injury to the anterior cruciate ligament itself, that places the menisci at future risk, and gives rise to the feeling that the "knee is not secure" or "may give out".
This test is performed with the patient lying in the supine position with the hip passively flexed to 30 degrees and it is important to abduct the hip to relax the iliotibial tract and allow the tibia to rotate. The examiner stands lateral to the patient on the side of the knee that is being examined. The lower leg and ankle is grasped maintaining 20 degrees of internal tibial rotation. The knee is allowed to sag into complete extension. The opposite hand grasps the lateral portion of the leg at the level of the superior tibiofibular joint, increasing the force of internal rotation. While maintaining internal rotation, a valgus force is applied to the knee while it is slowly flexed. If the tibia's position on the femur reduces as the knee is flexed in the range of 30 to 40 degrees or if there is an anterior subluxation felt during extension the test is positive for instability.
Pivot-shift is not straightforward to perform. For many with instability, the reproduction of instability is unpleasant and 'visceral'. Accordingly, having experienced it once, the patient is unlikely to relax enough for a second or confirmatory test. This is probably why the sensitivity of the three major knee exams is increased with general anesthesia.[2] Similarly, with meniscal involvement, such as a bucket handle tear of the medial meniscus,[3] range of motion may be limited and muscle guarding may produce a false negative result.
References
[edit]- ^ a b "Pivot Shift Test - Wheeless' Textbook of Orthopaedics".
- ^ van Eck CF, van den Bekerom MP, Fu FH, Poolman RW, Kerkhoffs GM (Aug 2013). "Methods to diagnose acute anterior cruciate ligament rupture: a meta-analysis of physical examinations with and without anaesthesia". Knee Surg Sports Traumatol Arthrosc. 21 (8): 1895–903. doi:10.1007/s00167-012-2250-9. PMID 23085822.
- ^ Kong KC, Hamlet MR, Peckham T, Mowbray MAS (1994). "Displaced bucket handle tears of the medial meniscus masking anterior cruciate deficiency". Archives of Orthopaedic and Trauma Surgery. 114 (1): 51–52. doi:10.1007/BF00454738. PMID 7696051.
- Starkey, C., & Ryan, J. (2003). The Knee. Orthopedic & Athletic Injury Evaluation Handbook (pp. 106). F.A. Davis Company
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Pivot-shift test
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The pivot-shift test is a dynamic physical examination maneuver used in orthopedics to evaluate anterolateral rotatory instability of the knee, primarily associated with anterior cruciate ligament (ACL) deficiency or rupture.[1] It reproduces the sensation of knee "giving way" that patients experience during pivoting activities, such as changing direction while running, by assessing the interaction between the ACL and secondary stabilizers like the anterolateral ligament and iliotibial band.[2] This test is considered one of the most specific clinical indicators for ACL injury, though its reliability depends on the examiner's experience and the patient's muscle relaxation.[3]
Developed in the late 20th century, the pivot-shift test was first systematically described by Galway and colleagues in 1972 as a way to detect combined anterior translation and internal rotation of the tibia relative to the femur.[1] Biomechanically, a positive test demonstrates anterior subluxation of the lateral tibial plateau in near-extension, which reduces spontaneously as the knee flexes beyond 20–30 degrees due to the tightening of the iliotibial band.[2] It is particularly valuable in both acute and chronic settings to confirm ACL tears, differentiate isolated ACL injuries from those involving additional restraints (such as the posterolateral corner), and evaluate the success of ACL reconstruction surgery.[3]
Clinically, the pivot-shift test's presence correlates with higher risks of postoperative instability, patient-reported symptoms, and accelerated osteoarthritis following ACL reconstruction.[1] It outperforms static tests like the anterior drawer in detecting functional instability but can be challenging in acute injuries due to pain or swelling, often requiring anesthesia for accurate assessment.[3] Despite its utility, inter-examiner variability highlights the need for standardized techniques and adjunct imaging like MRI for comprehensive diagnosis.[2]
Introduction
Definition and Purpose
The pivot-shift test is a dynamic physical examination maneuver used to assess anterolateral rotary instability of the knee joint. It reproduces the pivot-shift phenomenon, in which the tibia undergoes anterior subluxation relative to the femur when the knee is extended, followed by spontaneous reduction as the knee flexes, typically at 20° to 30° of flexion.[4][1] The primary purpose of the test is to evaluate for anterior cruciate ligament (ACL) deficiency, making it particularly valuable in chronic cases where static tests like the anterior drawer may be less reliable due to adaptive muscle guarding or secondary stabilization. It also aids in identifying combined ligamentous instabilities, such as those involving the anterolateral ligament (ALL) or posterolateral corner, which can exacerbate rotational laxity beyond an isolated ACL tear.[4][1] In clinical practice, the pivot-shift test is performed in outpatient settings to correlate with patient-reported symptoms of knee "giving way" during pivoting or deceleration activities, though it is often more accurately elicited under anesthesia when muscle relaxation enhances detection of subtle instabilities.[4][1]Historical Background
The term "pivot shift" was first coined in 1972 by H.R. Galway and colleagues in their seminal description of anterolateral rotary instability as a clinical sign of anterior cruciate ligament (ACL) deficiency.[5] This work, published in the Journal of Bone and Joint Surgery (British Volume), emphasized the test's ability to reproduce the subluxation and reduction of the lateral tibial plateau observed in ACL-insufficient knees during dynamic loading. The description built on prior 1960s observations of rotary subluxation, notably by D.B. Slocum and R.L. Larson, who in 1968 linked anteromedial and anterolateral rotatory instabilities to non-contact knee injuries and introduced clinical tests to assess them.[6] During the 1980s, the pivot-shift test underwent refinements to enhance its clinical reliability, including modifications to the maneuver and the development of structured grading systems to quantify the degree of instability.[7] These efforts addressed variability in examiner technique and subjective interpretation, with studies exploring biomechanical correlations to better understand the test's reproducibility under controlled conditions. Key advancements in the 1990s further integrated biomechanics, as researchers like those in a 1997 review analyzed the test's underlying joint mechanics, including tibial translation and rotation, to inform surgical decision-making for ACL reconstruction.[7] The early 21st century marked a shift toward quantitative evaluation, culminating in the 2012 Panther Global Summit, where international experts proposed a standardized pivot-shift protocol to reduce interobserver variability and facilitate sensor-based measurements.[1] This consensus, aligned with International Knee Documentation Committee (IKDC) guidelines, promoted the use of navigation systems and inertial sensors for objective assessment, paving the way for more precise outcome tracking in ACL injury management.[1]Anatomy and Pathophysiology
Knee Structures Involved
The anterior cruciate ligament (ACL) is the primary stabilizer of the knee evaluated by the pivot-shift test, with its posterolateral bundle playing a key role in resisting anterior tibial translation and internal tibial rotation.[8] The ACL consists of two functional bundles—an anteromedial bundle that primarily constrains anterior translation and a posterolateral bundle that provides rotational stability—arising from distinct but adjacent attachments.[8] Anatomically, the ACL originates from the lateral intercondylar ridge of the lateral femoral condyle, a shallow bony ridge located posterior and proximal to the lateral epicondyle, and inserts onto the anterior tibial plateau between the intercondylar eminences, spanning approximately 22 mm in width at the tibial footprint.[9][10] Secondary stabilizers include the anterolateral ligament (ALL), which extends from the lateral femoral epicondyle to the anterolateral tibia and acts as a restraint to internal rotation, particularly in conjunction with the ACL.[11] The iliotibial band (ITB), a thick fascial band running along the lateral thigh from the iliac crest to the lateral tibia, contributes to varus and rotational stability through its tensioning across the knee.[12] The lateral collateral ligament (LCL), also known as the fibular collateral ligament, originates from the lateral femoral epicondyle and inserts onto the fibular head, providing lateral stability against varus forces and external rotation.[13] Posterolateral corner (PLC) structures, including the popliteus tendon (which originates from the posterior tibia and inserts on the lateral femoral condyle) and the lateral head of the gastrocnemius (attaching to the posterior femur), form a fibro-osseous complex that resists posterior translation and varus rotation.[14][15] Additional contributors to knee stability encompass the meniscofemoral ligaments (anterior and posterior bands connecting the posterior horn of the lateral meniscus to the medial femoral condyle), which augment rotational control, and the lateral meniscus itself, which functions as a wedge-shaped structure to enhance joint congruence and prevent anterolateral subluxation.[1] Dynamic stabilizers, such as the quadriceps (via anterior pull on the patella and tibia) and hamstrings (through posterior tibial tension), provide neuromuscular modulation to anterior-posterior and rotational forces during knee motion.[16] These anatomical elements collectively underpin the knee's resistance to the combined translational and rotational loads assessed in the pivot-shift test.[1]Mechanism of the Pivot Shift Phenomenon
In an anterior cruciate ligament (ACL)-deficient knee, the pivot shift phenomenon arises from dynamic anterolateral rotatory instability, where the lateral tibial plateau subluxates anteriorly relative to the lateral femoral condyle in near full extension due to unopposed secondary restraints.[17] This subluxation occurs because the ACL normally resists anterior tibial translation and internal rotation, and its absence allows the tibia to shift forward under physiological loads, particularly when combined with valgus stress and axial compression.[18] The subluxation is driven by a combination of valgus force (typically 40-50 N), axial tibiofemoral load, and internal rotation of the tibia, which together promote anterior displacement of the lateral tibial plateau while the medial side remains relatively stable, creating a coupled rotary and translational motion.[18] External rotation of the femur can further exacerbate this instability by increasing the torsional stress on the lateral compartment.[17] As the knee flexes to 20-40°, reduction of the subluxation occurs abruptly, often producing a palpable "clunk," primarily due to the tightening of the iliotibial band (ITB), which shifts from an anterior to a posterior orientation relative to the lateral femoral epicondyle, exerting a posterior pull on the tibia.[18] This phenomenon frequently co-occurs with injuries to associated structures, such as anterolateral ligament (ALL) tears, which contribute to persistent rotatory laxity by failing to constrain internal tibial rotation, and lateral meniscal ramp lesions, which heighten the risk of excessive subluxation by altering the lateral compartment's load distribution.[17] Biomechanically, the pivot shift replicates the non-contact pivoting injury mechanism of ACL rupture, where quadriceps contraction in hyperextension generates anterior shear forces on the tibia, leading to the initial tear and subsequent instability.[17]Performance of the Test
Patient Preparation and Positioning
The patient is positioned supine on an examination table to facilitate access and stability during the test.[19] The hip is flexed to approximately 30° and slightly abducted, which helps relax the iliotibial band (ITB) and allows for the necessary tibial subluxation to be assessed.[20] The knee begins in full extension, with the leg maintained in a relaxed state to minimize muscle guarding that could obscure findings.[19][21] Prior to performing the test, the examiner explains the procedure to the patient to alleviate anxiety and encourage muscle relaxation, as tension can lead to false-negative results.[21] The knee should be free of acute swelling or excessive pain that might restrict range of motion, and the test should be performed with caution and may be contraindicated in cases of suspected acute fractures or severe pain/guarding, as it could exacerbate injury or yield inaccurate results due to muscle tension.[16] The examiner typically sits or stands at the foot of the table, placing one hand on the distal femur to control internal rotation and the other on the proximal tibia or foot to apply valgus stress and axial load.[20][21] Additional considerations include testing both knees for comparative purposes and conducting the maneuver gently to avoid patient discomfort, as the test can only be reliably repeated a limited number of times due to increasing guarding.[21][20]Step-by-Step Technique
The pivot-shift test is performed with the patient supine and the knee starting in full extension, following a standardized sequence to assess anterolateral rotatory instability.[22][4]- Stabilize the distal femur with one hand to prevent movement, while using the other hand to apply approximately 20° of internal rotation to the tibia by grasping the foot or ankle.[4]
- With the knee in full extension, apply a valgus force and axial compression across the joint using the hand on the lower leg.[4]
- Slowly flex the knee from 0° to 90° while maintaining the valgus force, axial load, and tibial internal rotation; the reduction typically occurs at 20°-40° of flexion.[22][4]